Solar panels

[MikeFromMesa1]

I have been looking at RVs for the last 2 weeks trying to decide on which model to trade up to and one of the things I am interested in is adding solar. My old 2005 class B RV does not have solar and I wanted to make sure that the new one does, so I made sure to check on what kind and how many solar panels were installed on the RVs I looked at. What I found puzzled me.

One of the (used) 2017 models I looked at had 2 solar panels which seemed to be thin and flexible. While I could not reach them from the back RV ladder they looked like they were perhaps 1/4 inch thick and looked as though they were flexible. They also looked like they were glued to the top of the RV but since I could not get to them I could not really tell.

The (new) 2018 version of the same RV make and model had what I normally think of as solar panels - 2 thick and hard panels, both perhaps 1 inch thick, metal sided and covered with some translucent hard material. These were attached to what looked like a luggage rack on the top of the RV.

Can anyone tell me the differences between these two solar panel types? My first thought was that perhaps the soft and flexible (looking) solar panels were a newer design, but they were on the older RV, not the newer one, so perhaps they were a design that did not work properly and were being replaced in the newer models? Or perhaps they were an after-market version? Or something else? The difference does not really worry me, but it does make me curious.

 

[Optimistic Paranoid]

Flexible panels have been around for a while.  They are lighter than rigid panels, and if you have a curved roof, they can be easier to install.

Some people think that by gluing these panels down, there are less holes in the roof compared to the rigid panel installations, but if the riigid panes are installed and sealed correctly, this should never be a problem.

They are usually somewhat more expensive than rigid panels.  They make a lot less of them, so economy of scale can't kick in.

They are usually a bit less efficient than rigid panels.  I've seen figure online that suggest that rigid panels are 14 to 17 percent efficient, whereas flexible panels are 11 to 13 percent efficient.

To my mind, the biggest problem is heat.  Panels in the sun get hot.  Rigid panels, with an air space under them, have a lot more exposure to the air, so they will run cooler than panels glued down to the roof. This is probably part of the efficiency problem - the hotter a panel gets, the less power it produces.  (All specifications for panel volts, amps, and so on are specified at 77 degrees)  But I worry about what the hot panels in contact with the roof are doing to the roof's surface, especially if it's some kind of rubber roof.

For that reason alone, I wouldn't have them myself.  Of course, YMMV.

 

[MikeFromMesa1]

Flexible panels have been around for a while.  They are lighter than rigid panels, and if you have a curved roof, they can be easier to install.

Some people think that by gluing these panels down, there are less holes in the roof compared to the rigid panel installations, but if the riigid panes are installed and sealed correctly, this should never be a problem.

They are usually somewhat more expensive than rigid panels.  They make a lot less of them, so economy of scale can't kick in.

They are usually a bit less efficient than rigid panels.  I've seen figure online that suggest that rigid panels are 14 to 17 percent efficient, whereas flexible panels are 11 to 13 percent efficient.

To my mind, the biggest problem is heat.  Panels in the sun get hot.  Rigid panels, with an air space under them, have a lot more exposure to the air, so they will run cooler than panels glued down to the roof. This is probably part of the efficiency problem - the hotter a panel gets, the less power it produces.  (All specifications for panel volts, amps, and so on are specified at 77 degrees)  But I worry about what the hot panels in contact with the roof are doing to the roof's surface, especially if it's some kind of rubber roof.

For that reason alone, I wouldn't have them myself.  Of course, YMMV.

I knew none of this as I had not really researched solar panels but your comments make me wonder if that is why Winnebago went from flexible to rigid. The flexible panels looked a lot lighter and seemed to offer less wind resistance since they were almost completely flat on the roof. The rigid ones are mounted on roof rails and sit perhaps 2 inches off the roof, and I do wonder how the flexible ones can handle the summer heat here in Arizona as it does get into the mid to upper 110s in July and August (although I usually try to get out of the area during part of the summer).

I also can not help but wonder if the added wind resistance might lower my fuel mileage. It is a small sample but I seemed to get better economy test driving the 2017 with the flexible panels compared to the 2018 with the rigid panels.

 

[Optimistic Paranoid]

Renogy - a fairly well know supplier of solar panels and accessories - did a voluntary recall of some of their flexible panels because of the heat issue.  See:

https://www.renogy.com/voluntary-product-recall/

Oh, and while you're on the Renogy site, take a look at the comparison pop up Renogy has for their solid vs flexible panels.  They say the flexible panels are less resistant to snow, wind, and high impact loads.  (by which I guess they mean hail strikes?)

 

[Kevin Means]

One of the problems with flexible (thin film) solar panels, is that if they're installed over a low spot on the RV's roof, which is not uncommon, the panel will take on the shape of the roof, including the low spot. Moisture (rain, dew etc.) will pool in the low spot and attract dust and other sediments. The build-up will eventually block enough sunlight to significantly reduce the panel's output.

The remedies are to get on the roof and clean them frequently, or install them on a flat piece of substrate and then mount the substrate to the roof. Basically, you end up with a rigid panel. Rigid panels aren't immune to the problem of pooling moisture and sediment build up, but it usually occurs around the edges of the panel where the "glass" meets the aluminum frame. You still have to clean them, but usually not as often.

Kev

 

[MikeFromMesa1]

One of the problems with flexible (thin film) solar panels, is that if they're installed over a low spot on the RV's roof, which is not uncommon, the panel will take on the shape of the roof, including the low spot. Moisture (rain, dew etc.) will pool in the low spot and attract dust and other sediments. The build-up will eventually block enough sunlight to significantly reduce the panel's output.

The remedies are to get on the roof and clean them frequently, or install them on a flat piece of substrate and then mount the substrate to the roof. Basically, you end up with a rigid panel. Rigid panels aren't immune to the problem of pooling moisture and sediment build up, but it usually occurs around the edges of the panel where the "glass" meets the aluminum frame. You still have to clean them, but usually not as often.

Fortunately the class B has a movable ladder so getting to the panels should not be that difficult, but what do you use to clean them? Just wash them down with a hose? Or is there some special solution I should use? I assume that I will need to take care not to scratch the surface when cleaning them.

 

[Kevin Means]

Our coach has six panels on the roof. Before I was able to tilt them, I climbed onto the roof and cleaned them with a mild glass cleaner. Now that I can tilt them, I just stand next to the RV and rinse them off with my pressure washer. After all the water runs off, I lower the panels back down. Letting the water run off before lowering the panels really helps prevent dirt from gathering on them again. They probably don't get quite as clean as when I was cleaning them with the glass cleaner, but I don't have to get on the roof anymore, and I haven't seen any difference at all in the panel's output.

Kev

 

[Memtb]

    Kevin, I think if you were boondocking in the (more) northern latitudes during the fall/winter, the ability to ?tilt?,  truly comes into play. Short days, long nights, with the sun ?low? in the southern sky....having them face the sun is a big plus!

 

[Kevin Means]

Absolutely! Even in Southern Arizona, in November and March we run them at about a 40 degree tilt, but in January, they're at 60 degrees - even as far south as Quartzsite. Tilting them makes a huge difference, especially in the winter months.

Kev